About new Sims automatically added during a long game

The game tends to have problems with balancing sims from different packs when it is generating new sims. Which has lead previously to things like a lot city living sims getting spawned and lately too many Island Living sims.

You can usually tell what type of sim it is by their names. Base Game sims, City Living sims, Island Living sims etc have separate lists for their names.

Maybe you are not getting many base game sims in your game.